Color Management: various improvements and fixes for image saving

* Respect the image file color space setitng for saving in various cases where
  it was previously ignored. Previously it would often use the sRGB or Linear
  color space even when not selected.
* For the Save As operator, add a Color Space option in the file browser to
  choose the color space of the file. Previously this was chosen automatically,
  now it's possible to e.g. resave a Linear image as Linear ACES.
* When changing the file format, the colorspace is automatically changed to an
  appropriate color space for the file format. This already happened before, but
  there was no visibility or control in the operator settings for this.
* Don't change color space when using the Save operator to save over the same
  file.
* Fix missing color space conversion for 16 bit PNGs, where it assumed wrongly
  assumed ibuf->rect would be used for saving. Add BKE_image_format_is_byte to
  more accurately test this.

Fixes T74610

Ref T68926

Differential Revision: https://developer.blender.org/D14899

1 files changed, 70 insertions, 12 deletions

diff --git a/source/blender/blenkernel/intern/image_save.cc b/source/blender/blenkernel/intern/image_save.cc
index 0fd997c3a9b..106384643df 100644
--- a/source/blender/blenkernel/intern/image_save.cc
+++ b/source/blender/blenkernel/intern/image_save.cc
@@ -121,9 +121,16 @@ bool BKE_image_save_options_init(ImageSaveOptions *opts,
       opts->im_format.stereo3d_format = *ima->stereo3d_format;
       opts->im_format.views_format = ima->views_format;
 
+      /* Render output: colorspace from render settings. */
       BKE_image_format_color_management_copy_from_scene(&opts->im_format, scene);
     }
 
+    /* Default to saving in the same colorspace as the image setting. */
+    if (!save_as_render) {
+      BKE_color_managed_colorspace_settings_copy(&opts->im_format.linear_colorspace_settings,
+                                                 &ima->colorspace_settings);
+    }
+
     opts->im_format.color_management = R_IMF_COLOR_MANAGEMENT_FOLLOW_SCENE;
 
     if (ima->source == IMA_SRC_TILED) {
@@ -177,11 +184,57 @@ bool BKE_image_save_options_init(ImageSaveOptions *opts,
     }
   }
 
+  /* Copy for detecting UI changes. */
+  opts->prev_save_as_render = opts->save_as_render;
+  opts->prev_imtype = opts->im_format.imtype;
+
   BKE_image_release_ibuf(ima, ibuf, lock);
 
   return (ibuf != NULL);
 }
 
+void BKE_image_save_options_update(ImageSaveOptions *opts, Image *image)
+{
+  /* Auto update color space when changing save as render and file type. */
+  if (opts->save_as_render) {
+    if (!opts->prev_save_as_render) {
+      if (ELEM(image->type, IMA_TYPE_R_RESULT, IMA_TYPE_COMPOSITE)) {
+        BKE_image_format_init_for_write(&opts->im_format, opts->scene, NULL);
+      }
+      else {
+        BKE_image_format_color_management_copy_from_scene(&opts->im_format, opts->scene);
+      }
+    }
+  }
+  else {
+    if (opts->prev_save_as_render) {
+      /* Copy colorspace from image settings. */
+      BKE_color_managed_colorspace_settings_copy(&opts->im_format.linear_colorspace_settings,
+                                                 &image->colorspace_settings);
+    }
+    else if (opts->im_format.imtype != opts->prev_imtype) {
+      const bool linear_float_output = BKE_imtype_requires_linear_float(opts->im_format.imtype);
+
+      /* TODO: detect if the colorspace is linear, not just equal to scene linear. */
+      const bool is_linear = IMB_colormanagement_space_name_is_scene_linear(
+          opts->im_format.linear_colorspace_settings.name);
+
+      /* If changing to a linear float or byte format, ensure we have a compatible color space. */
+      if (linear_float_output && !is_linear) {
+        STRNCPY(opts->im_format.linear_colorspace_settings.name,
+                IMB_colormanagement_role_colorspace_name_get(COLOR_ROLE_DEFAULT_FLOAT));
+      }
+      else if (!linear_float_output && is_linear) {
+        STRNCPY(opts->im_format.linear_colorspace_settings.name,
+                IMB_colormanagement_role_colorspace_name_get(COLOR_ROLE_DEFAULT_BYTE));
+      }
+    }
+  }
+
+  opts->prev_save_as_render = opts->save_as_render;
+  opts->prev_imtype = opts->im_format.imtype;
+}
+
 void BKE_image_save_options_free(ImageSaveOptions *opts)
 {
   BKE_image_format_free(&opts->im_format);
@@ -243,12 +296,17 @@ static void image_save_post(ReportList *reports,
     BLI_path_rel(ima->filepath, relbase); /* only after saving */
   }
 
-  ColorManagedColorspaceSettings old_colorspace_settings;
-  BKE_color_managed_colorspace_settings_copy(&old_colorspace_settings, &ima->colorspace_settings);
-  IMB_colormanagement_colorspace_from_ibuf_ftype(&ima->colorspace_settings, ibuf);
-  if (!BKE_color_managed_colorspace_settings_equals(&old_colorspace_settings,
-                                                    &ima->colorspace_settings)) {
-    *r_colorspace_changed = true;
+  /* Update image file color space when saving to another color space. */
+  const bool linear_float_output = BKE_imtype_requires_linear_float(opts->im_format.imtype);
+
+  if (!opts->save_as_render || linear_float_output) {
+    if (opts->im_format.linear_colorspace_settings.name[0] &&
+        !BKE_color_managed_colorspace_settings_equals(
+            &ima->colorspace_settings, &opts->im_format.linear_colorspace_settings)) {
+      BKE_color_managed_colorspace_settings_copy(&ima->colorspace_settings,
+                                                 &opts->im_format.linear_colorspace_settings);
+      *r_colorspace_changed = true;
+    }
   }
 }
 
@@ -314,12 +372,12 @@ static bool image_save_single(ReportList *reports,
 
   /* we need renderresult for exr and rendered multiview */
   rr = BKE_image_acquire_renderresult(opts->scene, ima);
-  bool is_mono = rr ? BLI_listbase_count_at_most(&rr->views, 2) < 2 :
-                      BLI_listbase_count_at_most(&ima->views, 2) < 2;
-  bool is_exr_rr = rr && ELEM(imf->imtype, R_IMF_IMTYPE_OPENEXR, R_IMF_IMTYPE_MULTILAYER) &&
-                   RE_HasFloatPixels(rr);
-  bool is_multilayer = is_exr_rr && (imf->imtype == R_IMF_IMTYPE_MULTILAYER);
-  int layer = (iuser && !is_multilayer) ? iuser->layer : -1;
+  const bool is_mono = rr ? BLI_listbase_count_at_most(&rr->views, 2) < 2 :
+                            BLI_listbase_count_at_most(&ima->views, 2) < 2;
+  const bool is_exr_rr = rr && ELEM(imf->imtype, R_IMF_IMTYPE_OPENEXR, R_IMF_IMTYPE_MULTILAYER) &&
+                         RE_HasFloatPixels(rr);
+  const bool is_multilayer = is_exr_rr && (imf->imtype == R_IMF_IMTYPE_MULTILAYER);
+  const int layer = (iuser && !is_multilayer) ? iuser->layer : -1;
 
   /* error handling */
   if (rr == nullptr) {